Chromium coated articles and method of preparing same



Patented Oct. 4, 1932 UNITED STATES PATENT OFFIOE LOUIS WEISIBERG AND WILLARDF. GREENWALD, OF NEW YORK, N. -Y., ASSIGNORS TO 'WEISBERG & GREENWALD, INC., OF

YORK

NEW YORK, N. Y., A CORPORATION OF NEW CHROMIUM COATED ARTICLES AND METHOD OF PREPARING SAME No Drawing.

This invention relates to the electrodeposition and particularly to the preparation of surfaces to receive a Wear-resisting coating of chromium.

Lead and lead alloys such as type metal and similar metals which are relatively soft are easily abraded, and consequently the exposed surfaces, rapidly destroyed. This is particularly true in the case of stereotype plates and slugs, which are made by casting a molten alloy of lead containing small amounts of hardening agents such as antimony.

Attempts have been made heretofore to deposit chromium on and thereby to protect soft metals by providing a wear-resisting surface, but it has not been possible to accomplish the depositionqof chromium successfully on such materials because the chromium will not adhere to the base metal. The procedure often employed in chromium plating of first depositing a flash coating of copper or nickel does not avoid the difficulty, because copper and nickel do not form a satisfactory bond with metals such as lead, and consequently do not afford a proper base for the chromium.

It is the object of the present invention to provide. a simple and effective procedure whereby chromium can be deposlted in a simple and satisfactory manner upon a surface of a soft metal such as lead or an alloy thereof to produce a Wear-resisting chromium surface which adheres to the underlying metal and affords a surface capable of re-. sisting Wear.

Another object of the invention is the provision of a method for depositing chromium satisfactorily on stereotype printing plates andslugs and other similar objects, Whether prepared by the stereotype process or otherwise, and the provision also of a printing surface having a type metal base and an adhering coating of chromium thereon.

The object of the invention is accomplished by suitably cleaning the surface of the article to be coated andthen dipping it into an aqueous bath containing a mercury salt. For this purpose, solutions of mercuric cyanide and sodium cyanide or mercuric chloride and amwhen subjected to wear, are

Application filed August 1, 1930. Serial No. 472,487.

a suitable mercury salt results in the formation of an amalgam of mercury'and lead on the surface of' the article to be treated.

The surface carrying the lead-mercury amalgam is then brushed thoroughly until it is clean, and is disposed in a suitable electrolytic bath capable of depositing, through the action of the electric current, a coating of a metal capable of amalgamating with mercury, such as brass, upon the surface. The mercury present in the treated surface amalgamates with the 'zinc in the brass which is deposited on the surface, thus giving a per foot bond between thebase metal and the brass deposit. The surface may be cleaned again and is then ready for the deposition of the chromium, which adheres to and forms a coherent deposit upon the brass coating to afford a hard, wear-resisting surface.

The invention will be described particularly with reference to the treatment of stereotype plates and slugs, although the procedure may be employed for the deposition of chromium upon any article the exposed surface of which consists of a metal capable of amalgamating with mercury. A stereotype plate may be prepared in the usual manner by casting asuitable type metal alloy having abasis of lead in the usual matrix. In the ordinary stereotype process a matrix of paper is employed. The same principle is used, however, in the preparation of linotype and monotype slugs and in the casting of ordinary type.

The stereotype plate, for example, is cleaned carefully to remove any adhering foreign materials and is then dipped into an aqueous bath containing for example 8 to 10 grams per liter of mercuric cyanide with.

60 grams per liter of sodium cyanide, or 7.5 grams per liter of mercuric chloride with the addition of 4 grams per liter of ammonium chloride. The salts of mercury mentioned are best adapted for the practice of the invention, butothers may be utilized. The dipping of the plate in the mercury bath results immeprintmg.

diately in the formation of the film of lead amalgam on the surface of the plate. The surface is brushed thoroughly to remove any foreign particles adhering thereto and is then plated with brass.

We may employ any suitable brass plating procedure such as that set forth, for example, in Principles of Electroplating and Electroforming by Blum and Hogaboom, 2nd edition, pages 379-389. Thus, we may employ a cyanide solution containing copper and zinc in the ratio of 20, with a total metal content of at least 22.5 grams per liter and a free cyanide content about one-fourth the total of combined cyanide. To this bath may be added from 30 to 60 grams per liter of sodium carbonate. In this electrolyte, at a temperature'of about 40 C., the surface to be coated may be disposed as the cathode and subjected to the electric current with a cathode current density of about 2.8 amperes per sq. ft. We thus provide on the surface of the article to be coated a coating of brass in which the zinc is amalgamated with the lead amalgam previously formed on the surface, afiording a perfect bond with the underlying metal. After a suitable interval which is best determined by consideration of the amount of brass to be deposited on the surface, the oathode is removed and is again thoroughly cleaned. It is ready then for the deposit of chromium.

For the chromium plating, we prefer to employ the well-known Sargent solution containing, for example, from about 250 to 450 grams per liter of 'chromic acid (CrO and rom 2.5 to 4.5 grams per liter of sulphate radical represented by the addition to the chromic acid of sulphuric acid, chromium sulphate or an alkali sulphate such as sodium sulphate. The plate having the brass coating is disposed as the cathode in this solution,

- which is maintained at a temperature preferably between 30 and 45 C. It is subjected to the electric current at a cathode current density of, for example, 1 ampere per sq. in., for a brief period, suflicientto deposit a layer of chromium of the required thickness upon the surface of the plate. The chromium is deposited as a bright, dense and coherent layer and aflfords a hard, wear-resistin surface. It bonds perfectly with the under ying coating of brass and consequently will not flake when pressure is applied in the printing operation, nor is it aifected by the abrasive or corrosive properties of the 111k employed in In fact, it has been found that printing plates of lead or alloys"thereof,'when prepared and coated with chromium in the manner described, will remain sharp and clear and show no evidence of wear after produc-' ing manytimes the-number of impressions which can be obtained ordinarily .from thetype metal surface.

While the invention has been described with reference more particularly to the deposition of chromium on lead and alloys there'- of, it may be employed'also to similarly coat other metals and alloys thereof which are capable of forming amalgams, for example, fine and zinc alloys such as die casting aloys.

It is to be understood that the details of plating with brass and with chromium form no p'art'of the present invention and are subject to variation, the procedures described being merely typical of those well known in the art and adapted for the purpose of the invention. Theword"brass as used in the following claims is to be understood as including equivalent alloys and metals capable of forming amalgams. The words lead-containing metal are to be understood to include equivalent alloys and metals capable of forming amalgams.

- Various changes may be made in the details of the procedure without departing from the invention or sacrificing the advantages thereof.

We claim: I

1. The method of preparing asurface of lead-containing metal for chromium plating which comprises forming on the surface a layer of lead amalgam and electrolytically depositing brass thereon.

2a The method of coating with chromium a surface containing a metal capable of forming an amalgam which comprises subjecting the surface to a solution f a mercury compound, depositing a laye of brass on the surface and then depositing a layer of chromium thereon. v

3. A printing element having an underlying support of lead-containing metal, a surface of chromium and an intermediate layer of brass bonded to the lead-containing metal by an amalgam.

In testimony whereof we aflix our signatures.

LOUIS WEISBERG. WILLARD F. GREENWALD. 

